The present disclosure is directed to the improved process of Resin Transfer Molding (RTM), and more particularly use of a silicone elastomer (or functionally equivalent) intensifier inside the closed RTM tool to provide additional pressure during processing, thereby suppressing void formation within the laminate and providing uniform consolidation pressure to ensure wet-out of the fiber preform.
Fiber-reinforced polymer matrix composites (PMCs) are high-performance structural materials that are commonly used in applications requiring resistance to aggressive environments, high strength/stiffness, and/or low weight. Examples of such applications include aircraft components.
PMCs comprise layers of fibers that are bonded together with a matrix material, such as a polymer resin. The fibers reinforce the matrix, bearing the majority of the load supported by the composite, while the matrix bears a minority portion of the load supported by the composite and also transfers load across the fibers. In this manner, PMCs may support greater loads than either the matrix or fiber individually while exhibiting a more progressive failure. Furthermore, by tailoring the reinforcing fibers in a particular geometry or orientation, the composite can be efficiently designed to minimize weight and volume.
In liquid infusion processing, the reinforcing fibers are placed within a mold cavity or other mechanism for net-shape tooling in dry conditions, wetted with the matrix resin, and cured. Liquid infusion processing may be accomplished by a variety of techniques, including high and low pressure Resin Transfer Molding (RTM), Resin Film Infusion (RFI), Vacuum Assisted Resin Transfer Molding (VARTM) and Same Qualified Resin Transfer Molding (SQRTM).
The liquid infusion process may include any process by which the reinforcing fibers are first placed into a mold cavity, die head, or any other means of net shaped tooling and then wetted with the resinous matrix and cured.
Ceramic Matrix Composite (CMC) pre-ceramic polymer resins are not chemically stable when heated to temperatures below their pyrolysis temperature and therefore provide a challenge to molding a void/defect free laminate via liquid infusion processes.
Prior to, during and even after initial cure the pre-ceramic resins have demonstrated a propensity for release of gaseous compounds. These gases interfere with the complete filling of the fiber preform during resin injection, leading to a cured laminate with varying amounts, sizes and shapes of porosity. Unwanted porosity can also be formed for other reasons, such as improper filling of the resins. It is known that during Polymer Infiltration and Pyrolysis (PIP), large pores in the cured laminate will propagate to the pyrolyzed laminate and may remain open within the laminate through final densification.
It is therefore desirable when using CMC pre-ceramic polymerresin to be able to cure a laminate by liquid infusion such that large pores are not present and the gas/porosity evolution is either suppressed or results in very small, finely dispersed porosity.